1. Field of the Invention
The invention relates to an impedance-matching circuit for a multiband power amplifier, using an impedance-matching circuit with one-to-multiple path to efficiently transmit a radio frequency (RF) from an input port to the corresponding multi-ports without spurious effect.
2. Description of Related Art
In wireless communication, multiband operation is widely employed. Typically, a power amplifier is used to operate in different bands, as shown in FIG. 1. In addition, the structure of one power amplifier per band can be used (not shown). As shown in FIG. 1, a dual-band GSM/DCS radiotelephone with a power amplifier 120 can use both the Global System for Mobile Communications (GSM), which operates at 900 MHz, and the Digital Communications System (DCS), which is similar to GSM except that it operates at 1800 or 1900 MHz. Such a structure can save costs but the circuitry is complicated. In this example, the amplifier 120 outputs the proper impedance, e.g. 50 xcexa9, matched to the impedance of the multiband antenna through the matching circuit 140 so that the input signal 110 generates the proper operating power output 151, 152. For this purpose, switches or resonators are added to the matching circuit. Thus, the circuit becomes more complicated.
Accordingly, multiple output ports are further employed. For this example, the use of multiple output ports has the advantage of easily connecting different filters and transmitting/receiving signal from switch. To build up a multiband-matching network with multiple output ports, a separate, switched highpass- and lowpass-matching network is utilized with output from an amplifier. However, such a structure requires a switch with power handling capability and lower insertion loss, occupying more space and raising costs.
Therefore, a solution is further subjected to the switch problem. Different operating band resonators are used in the multiband application of multiple transmitting paths (U.S. Pat. No. 5,969,582). However, a problem in this circuitry design is lack of flexibility.
Accordingly, an object of the invention is to provide a multiband matching circuit with an input port and multiple output ports, which has the feature of circuitry flexibility to create the best impedance matching.
The invention provides a multiband matching circuit with an input port and multiple output ports. The matching circuit includes a plurality of frequency paths; and a short circuit for filtering out the RF signals in other remaining bands. The reactance used in every path provides different bands with different amplitudes and signs (inductance or capacitance) so that the buffer resonator is generated with the preferred flexibility of multiband match.